New Jersey State Police said Friday they were still investigating the cause of Leffler's accident at the 0.625-mile dirt oval.

According to his team, Leffler was wearing a Simpson Hybrid head and neck restraint system, which is one of six approved for use in NASCAR. A blunt force injury occurs when an object strikes the body with force causing compression of tissue. Head and neck restraints are designed to prevent injuries resulting from deceleration trauma when the body is moving and strikes another moving or stationary object, causing stretching or tearing of body tissue.

Leffler, a versatile driver who won championships in open-wheel divisions and attempted at least one full season in each of NASCAR's three national series, had to be extricated from the car after striking a wall, New Jersey State Police Sgt. Adam Grossman told USA TODAY Sports.

Leffler made 73 starts in the Sprint Cup Series, finishing last in his final event after completing eight laps Sunday at Pocono Raceway. He won twice in the Nationwide Series and once in the Camping World Truck Series.

The Long Beach native was affectionately known as "LEFturn" and had the nickname stenciled above his driver's side window.